This release is the stable version of the 2.1.X series tree.
Since the last beta release (2.1.3) the following changes were made:

1) Major updates to documentation of the forum, which include the addition of a section on how to upgrade, how to report bugs as well as documentation on the Theme Manager control panel. A few other fixes such as updated CVS information were made as well.

2) Fixed a bug with Private Messages that would display the wrong user name on the mouse-overs captions for the online/offline icon.

3) Added a download link to VBulletin to FUDforum conversion script.

4) Fixed a a few bugs in the compiler, that would mess up if many themes were to be compiled within the same script (upgrade.php).

5) Added code to the installer to verify that the user has MySQL or PostgreSQL support and in case of PostgreSQL make sure that PHP version is >4.2.0

More details inside the CHANGELOG file, which can be found at the bottom of the download page.